A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
The present invention is directed to an electrical distribution selectivity analysis method and apparatus.
Power distribution devices are well known in the art. In typical power distribution systems, selectivity is desired generally to minimize nuisance tripping. FIG. 1 generally shows a two tier selective system 40. Selective system 40 comprises a source 41, an upstream protection device 42, a downstream protection device 44 coupled to a load 45, and a downstream protection device 46 coupled to a load 47. Any number of additional downstream protection devices 44 with corresponding loads 47 may be included in system 40. Generally, each protection device 42, 44 or 46 is a circuit interrupter (e.g., in a single phase power system) or a multiple pole circuit breaker (e.g., in a multiple phase power system). These circuit breakers can be any type, including but not limited to low voltage, medium voltage, high voltage, air, or vacuum breakers for residential, commercial or industrial uses. Source 41 is any power source or combination of power sources including but not limited to outside power feeds, generators, transformers, or uninterruptible power supplies. Loads 45, 47 can be any load or combination of loads including but not limited to motors, lamps, ballasts.
A conventional circuit breaker includes a pair of contacts which allows circuit current to pass from one contact member to another contact member. An objective of these devices is to carry nominal rated current at very low loss and have momentary circuit current withstand levels, commonly referred to as xe2x80x9cpopping levelsxe2x80x9d. A withstand level is generally the level of circuit current that may pass through the circuit breaker before a fault condition is realized causing the contacts to open to prevent circuit current from passing through the contacts. When the contacts open, circuit current is prevented from flowing from one contact member to the other and therefore, circuit current is prevented from flowing to a load which is connected to the device. By having these momentary circuit current withstand levels, operation under high inrush loads, common with motors and transformers, is permitted. Accordingly, these devices need to have momentary circuit current withstand levels so that they may be properly used with such high inrush loads to protect the loads and the overall electrical system.
Downstream device 44 is rated to meet the demands of load 45, e.g., 20xc3x97(twenty times) rated circuit current maximum. When load 45 exceeds this rating, which is likely only when a fault occurs, device 44 would then rapidly transition to a current limiting position. In the current limiting position, downstream device 44 has a reduced circuit current let-thru which in turn reduces stresses on the entire system 40. By reducing these stresses on system 40, the devices of load 45 are also protected and this is of particular interest if load 45 has a motor starter in the circuit thereof.
FIG. 2 is a plot of peak let-thru current versus prospective current of downstream device 44 and upstream device 42 in a current limiting position in accordance with the present invention. Downstream device 44 is in a current limiting position when device 44 is under fault conditions which are circuit current conditions substantially above the withstand level. In this position, downstream device 44 keeps the let-thru circuit current below the withstand level of the upstream device 42, as shown in FIG. 2. Because upstream device 42 can be of the same design as downstream device 44 and have a high withstand, it does not trip and the remainder of the system 40 remains in service. If upstream device 42 did not have a sufficiently high withstand level, then upstream device 42 would be prone to tripping and such tripping would cause the remainder of the system 40 to be out of service. By reducing the circuit current let-thru, downstream device 44 reduces the stresses on the entire system 40 and thereby protects the devices of load 47 as well. The plots represented on FIG. 2 represent ideal system behavior. Even if the ideal behavior is not attained, selectivity is still possible generally as long as the let-through of downstream device 44 remains below the trip response of upstream device 42. However, in non-ideal systems, the behavior cannot be analyzed with conventional techniques because the current through downstream device 46 will also be effected by the voltage generated by the upstream device.
Turning now to FIGS. 3 and 4, an exemplary multi-pole circuit breaker 50 that can be an upstream protection device 42, a downstream protection device 44, and/or a downstream protection device 44 are shown. Circuit breaker 50 generally includes a molded case including a top cover 52, a mid cover 54 and a base 56. A plurality of cassettes 58, 60 and 62 are disposed within base 56. An operating mechanism 64 is disposed atop cassette 60. Cassettes 58, 60 and 62 are commonly operated via a set of cross bars 66, 68. The crossbar 66 is disposed through an opening 70 in a portion of operating mechanism 64.
A line side contact strap 72 and a load side contact strap 74 extends from each cassette 58, 60 and 62 for connection with a power source and a protected circuit and/or load, respectively. A current transformer 76 is arranged relative to each line side contact strap 72. Current transformer 76 is coupled (not shown) to a trip unit 78 positioned within mid cover 54. Optionally, a rating plug (not shown) can be interfaced with trip unit 78 to change the settings of circuit breaker 50.
Trip unit 78 includes an actuator 80. Actuator 80 can be, for example, a flux actuator that operates substantially as described in U.S. Pat. No. 6,211,758 entitled xe2x80x9cCircuit Breaker Accessory Gap Control Mechanismxe2x80x9d, U.S. Pat. No. 6,172,584 entitled xe2x80x9cCircuit Breaker Accessory Reset Systemxe2x80x9d, and in U.S. Pat. No. 6,211,757 entitled xe2x80x9cFlux Actuatorxe2x80x9d.
Operating mechanism 64 includes a toggle handle 82 extends through openings within top cover 52 and mid cover 54. Toggle handle 82 provides external operation of operating mechanism 64. Operating mechanism 64 operates substantially as described in U.S. Pat. No. 6,346,868 entitled xe2x80x9cCircuit Interrupter Operating Mechanismxe2x80x9d and in U.S. Pat. No. 6,087,913 entitled xe2x80x9cCircuit Breaker Mechanism for a Rotary Contact Assemblyxe2x80x9d.
Cassettes 58, 60, 62 are typically formed of high strength plastic material and each include opposing sidewalls 84, 86. Sidewalls 84, 86 have a pair of arcuate slots 88, 90 positioned and configured to receive and allow the motion of cross bars 66, 68 by operating mechanism 64. Examples of a rotary contact structures that may be operated by operating mechanism 64 are described in more detail in U.S. Pat. No. 6,114,641 entitled xe2x80x9cRotary Contact Assembly For High-Ampere Rated Circuit Breakersxe2x80x9d and U.S. Pat. No. 6,396,369, entitled xe2x80x9cLaterally Moving Line Strapxe2x80x9d, U.S. Pat. No. 6,175,288 entitled xe2x80x9cMagnetic Supplemental Trip For A Rotary Circuit Breakerxe2x80x9d, and U.S. Pat. No. 6,366,438 entitled xe2x80x9cRotary Contact Armxe2x80x9d.
Referring now to FIG. 5, a partial view of the inside of a cassette similar to cassettes 58, 60, 62 is shown. Each cassette 58, 60, 62 includes a rotary contact assembly 92. Rotary contact assembly 92 is disposed intermediate to line side contact strap 72 and load side contact strap 74. Line side contact strap 72 and load side contact strap 74 are configured as U-shaped reverse loop conductor straps. Line side contact strap 72 includes a stationary contacts 94 and load side contact strap 74 includes a stationary contacts 96. Rotary contact assembly 92 further includes a movable contact arm 100 having a set of contacts 102 and 104 that mate with stationary contacts 94 and 96, respectively. Furthermore, a quantity of ablative material (not shown) is provided adjacent to stationary contacts 94, 96. The ablative material can be, for example, a nonelectrically conducting material such as a glass melamine or a glass polyester resin, or a cotton base fiber on the surface of a suitable resin such as a phenolic.
A pair of arc handling portions 106, 108 are disposed proximate to line side contact strap 72 and load side contact strap 74, respectively. Arc handling portions 106, 108 typically contain an arc chute configured to divert a gas flow of the ablative material (described further herein) out of cassette 58, 60, 62, substantially as described in U.S. Pat. No. 4,733,032 entitled xe2x80x9cElectric Circuit Breaker Arc Chute Compositionxe2x80x9d and in U.S. patent application Ser. No. 09/602321 entitled xe2x80x9cArc Chute Assembly for Circuit Breaker Mechanismsxe2x80x9d.
Contact arm 100 is mounted within a rotor 110. A pair of openings 112, 114 are disposed proximate to the outer perimeter of rotor 110. Openings 112, 114 are configured to accept crossbar is 66, 68.
Rotor 110 includes a pair of opposing faces 116 (one of which is shown in FIG. 3) and is configured to have a set of slots 118 disposed centrally across each face 116. A contact spring 120 is disposed in each slot 118. Each contact spring 120 is arranged on a pair of spring pins 122, 124.
Referring now to FIG. 6, a side view of rotary contact assembly 92 is shown intermediate to line side contact strap 72 and load side contact strap 74. Spring pins 122, 124 are disposed on top of and at the bottom of, respectively, contact arm 100 via a pair of pivotal links 126 at the top and links 128 to the at the bottom. Spring pins 122, 124 are positioned within pin retainer slots 130, 132 formed in rotor 110 (intermediate to each face 116). Pivotal links 126,128 pivot upon pivot pins 134, 136, respectively.
Contact arm 100 and rotor 110 pivot about a common center 138. Center 138 typically is a cylindrical feature protruding from a central portion of contact arm 100 and is captured within rotor 110 to allow contact arm 100 to rotate separately from rotor 110.
Spring pins 122, 124 are positioned in line (co-linear) with center 138 so that the spring force, indicated by arrows H, exerted between spring pins 122, 124 is directed to intersect the axis of rotation of movable contact arm 100. The force H is transferred to movable contact arm 100 via spring pins 122, 124, links 126,128, and pivot pins 134,136. Pivot pins 134,136 are offset from the line created by spring pins 122, 124 and center 138. This offset allows the force H to rotate movable contact arm 100. The rotation of movable contact arm 100 urges movable contacts 102, 104 toward fixed contacts 94, 96, generating a contact pressure between movable contacts 102, 104 and fixed contacts 94, 96. Because the force H is centered through the rotational axis of movable contact arm 100, the force of movable contact 102 onto fixed contacts 64 is substantially equal to the force of movable contact 104 onto fixed contact 96.
During quiescent operation, contacts 102 and 104 are mated with stationary contacts 94 and 96 and contact arm 100 is in the xe2x80x9cclosedxe2x80x9d position. That is, current flows from line side contact strap 72 to load side contact strap 74, through contact arm 100.
Reverse loop forces are created at the interface of fixed and movable contacts 94, 96, 102, 104, generally by current through the U-shaped line side contact strap 72 and/or load side contact strap 74. Furthermore, due to the non-uniform current flow through movable contact arm 100, constriction forces are created through contact arm 100 and at the interface of fixed and movable contact 94, 96, 102, 104. This causes movable contacts 102, 104 to be urged apart from fixed contacts 94, 96. The force caused by magnetic repulsion acts against the contact pressure created by the contact springs 120, which, in the absence of such magnetic repulsion, tend to maintain the fixed and movable contacts 94, 96, 102, 104 in a xe2x80x9cclosedxe2x80x9d position.
Referring now to FIG. 7, fixed and movable contacts 94, 96, 102, 104 are in an xe2x80x9copenxe2x80x9d position. The condition represented in FIG. 5 occurs, when, for example, the loop forces and/or constriction forces exceeds the contact pressure exerted by rotor structure 92, including springs 120, whereby contact arm 100 is urged in the clockwise direction about center 138, while rotor 110 remains stationary. The rotation of contact arm 100 moves pins 134 and 136 around center 138 and toward the line of force H created by springs 120. The motion of pins 134 and 136 is translated to spring pins 122 and 124 via links 126 and 128, causing spring pins 122 and 124 to translate within slots 130 and 132 towards the outer perimeter of rotor 110. The translation of spring pins 122 and 124 acts against the force of springs 120.
When pins 134, 136 and center 138 are aligned with the force H, the xe2x80x9covercenterxe2x80x9d position is achieved. At this position, if the loop and constriction forces continue to overcome the force from spring 120, contact arm 100 will continue clockwise rotation about center 138 and remain xe2x80x9copenxe2x80x9d, as shown in FIG. 5,
At certain conditions e.g., xe2x80x9cpopping levelsxe2x80x9d or xe2x80x9cwithstand levelsxe2x80x9d (not shown), the loop and constrictive forces are high enough to overcome the contact pressure to separate the fixed and movable contacts 94, 96, 102, 104, but not high enough to bypass the xe2x80x9covercenterxe2x80x9d position.
Referring now to FIG. 8, the interface between actuator 80 and operating mechanism 64 is shown. Operation of actuator 80 allows fixed and movable contacts 94, 96, 102, 104 to be separated even when the contact pressure exerted generally by contact springs 120 are not overcome by constriction forces and/or loop forces.
Actuator 80 includes a magnetic plunger assembly 140 that is coupled to, for example, circuitry within trip unit 78. Magnetic plunger assembly 140 includes a plunger 142 that moves from a retracted position to an extended position. An actuator linkage assembly 144 having an actuator trip tab 146 is positioned proximate to plunger 142.
Operating mechanism 64 includes a latch assembly 148, described in more detail herein. Latch assembly 148 includes a secondary latch trip tab 150 extending generally outwardly from operating mechanism 64 and positioned proximate to actuator trip tab 146 when circuit breaker 50 is assembled. Toggle handle 82 is interconnected with a mechanism linkage assembly 152, further described herein, which generally interfaces crossbar 66 through opening 70.
During quiescent operation, plunger 142 within actuator 80 is retracted. The fixed and movable contacts 94, 96, 102, 104 are closed such that current flows from line side contact strap 72 to load side contact strap 74.
Upon occurrence of a trip event (e.g., a short circuit, an overcurrent, or a ground fault), actuator 80 receives a trip signal generally outputted from circuitry within trip unit 78. The trip signal causes a magnetic flux within magnetic plunger assembly 140 to allow plunger motion from the retracted position to the extended position. When moved to the extended position, plunger 142 contacts a portion of actuator linkage assembly 144, which, in turn, causes displacement of actuator trip tab 146. The displacement of actuator trip tab 146 contacts secondary latch trip tab 150, which releases latch assembly 148 and causes mechanism linkage assembly 152 to translate crossbar 66. The translation of crossbar 66, in turn, causes rotary contact assembly 92, including contact arm 100, to rotate such that movable and fixed contacts 94, 96, 102, 104 become separated such that current is prevented from flowing from line side contact strap 72 to load side contact strap 74.
Referring now to FIGS. 9 and 10, certain components of operating mechanism 64 will now be detailed. Operating mechanism 64 has operating mechanism side frames 154 configured and positioned to straddle cassette 60.
Toggle handle 82 (not shown in FIGS. 9 and 10) is rigidly interconnected with a handle yoke 156. Handle yoke 156 includes U-shaped portions 158 that are rotatably positioned on a pair of pins 160 protruding outwardly from side frames 154. Handle-yoke 156 includes a roller pin 162 disposed intermediate to the sides of handle-yoke 156.
Handle yoke 156 is connected to a set of mechanism springs 164 by a spring anchor 166 generally supported within a pair of openings 168 in handle yoke 156 and arranged through a complementary set of openings 170 on the top portion of mechanism springs 164.
A pair of cradles 172 are disposed adjacent to side frames 154 and pivot on a pin 174 disposed through an opening 176 approximately at the end of each cradle 172. An opening 204 and an arcuate slot 180 are generally centrally disposed on cradles 172. Each cradle 172 is positioned generally under roller pin 162 and supported in an arcuate slot 182 on each side frame 154 by a rivet 184. Each cradle 172 includes an arm 186 that depends downwardly and a latch surface 188 generally disposed above arm 186.
Latch assembly 148 includes a primary latch 190 and a secondary latch 192. Primary latch 190 includes a pair of side portions 194 interconnected by a central portion 196. Central portion 196 includes a pair of extension portions 198 extending beyond side portions 194. Each side portions 194 includes an upper side portion 200 and a bent leg 201 at the lower portion thereof. Each upper side portion 200 includes a latch surface 202. An opening 204 is positioned on each side portion 194 so that primary latch 190 is rotatably disposed on a pin 206. Pin 206 has opposing ends secured to each side frame 154.
Secondary latch 192 is positioned to straddle side frames 154. Secondary latch 192 is pivotally mounted upon frames 154 via a set of pins 208 that are disposed in a complementary pair of notches 210 on each side frame 154. A spring 212 is disposed between an opening 214 on secondary latch 192 and a frame cross bar 216 disposed between frames 154. Secondary latch 192 includes a pair of latch surfaces 218, generally positioned proximate to latch surfaces 202 when primary latch 190 and secondary latch 192 are engaged, as described herein. Additionally, secondary latch 192 includes secondary latch trip tabs 150 that extend perpendicularly from operating mechanism 64.
Mechanism linkage assembly 152 includes a pair of upper links 220 and lower links 222. A bottom portion 224 of each upper link 220, generally U-shaped, and an opening 226 on each lower links 222, are commonly pivotable about an outer surface of a side tube 228. A side tube 228 is disposed on each side frame 154.
A pin 208 is disposed through a pair of openings 169 at the lower end of each mechanism spring 164, a central tube 232, and into each side tube 228. Therefore, each side tube 228 is a common pivot point for upper link 220, lower link 222 and mechanism springs 164.
Upper links 220 are interconnected with cradles 172 via a first rivet pin 234 disposed through opening 204 and a second rivet pin 236 disposed through arcuate slot 180. First and second rivet pins 234, 236 attached to a connector 238 at an opposing face of each cradle 172.
Lower link 222 is interconnected with a crank 240 via a pivotal rivet 242 disposed through an opening 244 in lower link 222 and an opening 246 in crank 240. Crank 240 is positioned on a crank center 248 and has an opening 250 where crossbar 66 passes through into arcuate slot 88 of cassette 58, 60 and 62 and a complementary set of arcuate slots 252 on each side frame 154.
A weld block lever 254 is also disposed on each side frame 154. Weld block lever 254 interacts with a blocking projection 256 of handle yoke 156, and with a cam port on 258 of crank 240 when a particular rotary contact assembly is fixed or welded in the closed position. The operation of weld block lever 254 is described in more detail in U.S. Pat. No. 6,166,344 entitled xe2x80x9cCircuit Breaker Handle Blockxe2x80x9d.
When latch assembly 148 is set, by urging handle yoke 156 in the counterclockwise direction as oriented in FIG. 7, primary latch surfaces 202 rests against secondary latch surfaces 218 and primary latch extension portions 198 rest against cradle latch surfaces 188. Crossbars 66, 68 assist in holding rotor 110 in the xe2x80x9cclosedxe2x80x9d position, as seen in FIG. 4, because crank 240 is not caused to rotate by mechanism linkage assembly 152.
Also, urging handle yoke 156 in the counterclockwise direction translate a forced to mechanism springs 164, which drives pin 208 to the right so that a portion of upper link 220 and lower link 222 are in line. This causes crank 240 to rotate clockwise about crank center 248 thereby driving cross pin 66 to the upper end of arcuate slots 252 and rotating rotor 110 (including contact arm 100) clockwise about center 138 such that fixed and movable contacts 94, 96, 102, 104 are mated and current is allowed to flow through contact arm 100.
When latch assembly 148 is tripped, i.e. by actuator trip tab 146 contacting secondary latch trip tab 150, primary latch 190 is driven by mechanism springs 164 via the clockwise motion transmitted to cradles 172. Mechanism springs 164 also transmit a force via pin 208 to lower link 222, which causes crank 240 to rotate in the counter clockwise direction, thereby driving cross bar 66 and rotating rotors 110 within cassette 58, 60 and 62 so that contacts 102, 104 upon contact arm 100 are rapidly separated from stationary contacts 94, 96.
Automatic circuit protection against overload circuit conditions is provided by means of trip unit 78 located within mid cover 54. In certain circuit protection devices, trip unit 78 is an electronic trip unit. It is well known that trip unit 78 can be eliminated, or may comprise, e.g., a thermo magnetic trip unit. A rating plug can be included to allow the circuit interruption rating to be set by accessing the electronic trip unit without disassembling top cover 52 from mid cover 54. Electronic trip unit 78 generally receives an input from current transformer 76 and provides output to actuator 80 (i.e., a second type of interruption).
A block diagram of an exemplary electronic trip unit 78, including the input from each current transformer 76, is provided in FIG. 11. Current transformers 76 (one associated with each phase of current in a multi-phase system) provide inputs (in the form of a current) to trip unit 78 (indicated in FIG. 9 with dashed lines). In the example shown, trip unit 78 includes a signal conditioner 260, a power supply 262, a micro controller 264, a firing circuit 266, and an actuator 80.
The currents from current transformers 76 are coupled in parallel to power supply 262 and signal conditioner 260. Power supply 262 energizes signal conditioner 260, micro controller 264, and firing circuit 266. Signal conditioner 260 conditions current signal and feeds the current signal to micro controller 264. Generally, the signals fed to signal conditioner 260 are in analog form. These analog signals can be converted to digital signals with an analog-to-digital converter within signal processor 260, with an analog-to-digital converter within micro controller 264, or a combination of an analog-to-digital converter within signal processor 260 and an analog-to-digital converter within micro controller 264. Firing circuit 266 can be, for example, a low voltage power MOSFET. Control signals are sent from micro controller 264 to firing circuit 266. Upon a determination of a predetermined event, for example, an overcurrent condition, micro controller 264 provides a signal to firing circuit 266, which is energized by power supply 262 and outputs a trip signal to actuator 80. The trip signal to actuator 80 causes magnetic plunger assembly 140 to allow plunger motion from the retracted position to the extended position, which in turn causes plunger 142 to contact a portion of actuator linkage assembly 144 and displaces actuator trip tab 146. The displacement of actuator trip tab 146 contacts secondary latch trip tab 150, which releases latch assembly 148 and causes mechanism linkage assembly 152 to translate crossbars 66, 68 and separate movable and fixed contacts 94, 96, 102, 104 as described above.
To understand the behavior of these devices at both the system level and the component level, circuit breakers are positioned between a power source and a load, and various fault conditions are generated. The conditions of the breaker immediately before the breaker starts to opens, and during opening, are generally studied with current and voltage curves for each phase.
However, this approach can be time consuming, as the desired circuit breaker must be constructed and installed. Furthermore, the fault condition must be experimentally generated, which is also costly and time consuming.
An accurate model of a circuit breaker that will describe the conditions of the circuit breaker under various fault conditions is, therefore, desirable. Such a model will allow a user to build a virtual circuit interrupter or breaker and perform various studies and simulations regarding the behavior of the device.
An apparatus and method for analyzing an apparatus, typically an electrical distribution system is provided. In one embodiment, the apparatus and method is employed for analyzing selective electrical distribution systems. The apparatus is generally a software system including a solver system for generating an output from an input presented to the solver system. The input is a mathematical representation of at least a portion of the electrical distribution system. In certain embodiments, the input is presented to a model within the solver system. The model represents at least a portion of the electrical distribution system. The software system is capable of interfacing output data from one or more models with additional models for analyzing generally how devices within an electrical distribution system behave under certain conditions.
The software system may analyze several models simultaneously. For example, a first model and a second model each being mathematical representations of at least a portion of one or more circuit interruption devices within the electrical system can be provided. The input can be fed through the first model, and the output of the first model used as input for the second model. Alternatively, the input and the output of the first model can be fed as input for the second model. Numerous variations are possible.
Inputs to the system can be presented by an interface with a user. Additionally, inputs can be presented by an interface with a simulator system. For electrical systems, the input generally comprises a simulated power feed. When fault behavior is to be analyzed, the input further comprises a simulated fault is said simulated power feed. The simulator system generates the simulated power feed and fault at user defined parameters, including, but not limited to, closing angle, power factor, peak voltage and maximum current.